MicroLogix 1200 Communication Toggle Button

I don't have any prior experience with MicroLogix so the Communication Toggle Button is new to me. We currently have a few MicroLogix that are using the RS 232 port (Channel 0) to communicate to the HMI. I am needing upload from the PL C to make a slight modification to the program and download it back to the PLC.

The PLC is currently not communicating with me through my Serial to USB converter cable. I have read and found out about the Communication Toggle Button that will allow the PLC to flip back and forth from the User-Defined configuration and default configuration of the communication port. Once I toggle the communication button to default and am able to communicate and upload from the PLC, make my change and insert it back into the PLC, am I able to simply just toggle back the communication button so the PLC will communicate with the HMI as before through whatever protocol it was using before my change? Will it still revert back to the user-defined communication protocol?

That's what it was designed to do.
Toggling the switch should switch between modes.

Yes, that's exactly what it does.

When you press the DCOMM button and the DCOMM LED turns on, then the Channel 0 serial port is set for the default DF1 settings (Full Duplex point-to-point, 8/N/1 framing, 19200 baud, CRC error checking).

If you press the button again and the DCOMM LED extinguishes, the controller goes back to whatever settings the user program was configured to use.

I ran into this issue, too, a couple of weeks ago. Where is this DCOMM button? Next to the 8-pin mini din?


I ended up disconnecting the HMI, and plugging that HMI cable into a UIC adapter, to get online with that ML1200 PLC. Found out the channel 0 port was set for DH485.

The DCOMM button is to the right of the connector just under the trim pots.
See page 69 of this user manual https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1762-um001_-en-p.pdf